The objective of this work is to elaborate an immunosensing system which will detect and quantify Staphylococcus aureus bacteria. A gold electrode was modified by electrografting of 4-nitrophenyl diazonium, in situ synthesized in acidic aqueous solution. The immunosensor was fabricated by immobilizing affinity-purified polyclonal anti S. aureus antibodies on the modified gold electrode. Cyclic voltammetry (CV) and Faradaic Electrochemical Impedance Spectroscopy (EIS) were employed to characterize the stepwise assembly of the immunosensor. The performance of the developed immunosensor was evaluated by monitoring the electron-transfer resistance detected using Faradaic EIS. The experimental results indicated a linear relationship between the relative variation of the electron transfer resistance and the logarithmic value of S. aureus concentration, with a slope of 0.40 ± 0.08 per decade of concentration. A low quantification limit of ？CFU per ml and a linear range up to ？CFU per mL were obtained. The developed immunosensors showed high selectivity to Escherichia coli and Staphylococcus saprophyticus. 1. Introduction Staphylococcus aureus is a major human pathogen responsible for a broad range of diseases because it is able to produce heat-resistant toxins in food [1]. Foods that are frequently incriminated in staphylococcal poisoning include meat and meat products, milk, and water. The toxic chemical released by S. aureus is enterotoxin that has been found to be produced at a hazardous level for 108 cells per kg of food [2]. Therefore rapid, sensitive, and reliable methods to detect foodborne pathogens are increasingly necessary in health care today. Traditional methods for foodborne bacteria detection including polymerase chain reaction (PCR) [3], enzyme-linked immunosorbent assay [4], and those based on culture and colony counting [5] have been widely applied due to their high reliability. However, these methods suffer from obvious disadvantages: they are time consuming and require expensive equipment and complicated pretreatment, so they are difficult to use on site. Biosensor technologies play an increasingly important role in the detection of pathogenic bacteria because they present the great potential of satisfying the practical need for rapid, wearable, and low-cost detection [6]. Among biosensors, immunosensors are widely investigated for bacteria detection due to their specific advantages, such as high affinity and simple fabrication [6, 7]. In the literature, many recent studies focus on E. coli and Salmonella bacteria detection with different
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